The fabrication of prototypes has long been a technique employed to evaluate the conceptual and functional feasibility of articles proposed for manufacture. Traditional prototyping techniques have generally entailed designing a component, followed by the manufacture of tooling from which the prototype is produced. While computer-aided design (CAD) techniques have become widely used in the design of both prototype and manufactured components, the conventional reliance on manufactured tooling to physically produce a prototype has been the dominating factor in determining when a prototype will become available, particularly for prototypes having complex geometries.
To reduce this lead time, CAD techniques have become more fully integrated with computer-aided manufacturing (CAM) techniques to eliminate the requirement for prototype tooling. Such methods include "rapid prototyping" (RP) processes, which generally entail the fabrication of a prototype from a material that is selectively cured or fused to form a unitary prototype. With rapid prototyping techniques, the period between prototype design and delivery can often be drastically reduced from several months required to fabricate prototype tooling, to as little as a few days.
Variations of rapid prototyping processes exist, with primary differences being the type and condition of the material being used to form the prototype, and the manner in which the material is fused or cured. Various materials can potentially be used, including powdered plastics, metals and ceramics. One known process involves the use of a photosensitive polymer in a liquid form. The liquid polymer is contained in a vat and successively cured in a manner that results in cured layers being successively fused together to form a unitary prototype. Suitable materials for this particular process are those that can be cured through exposure to a high-intensity light source, such as a laser beam, and include such materials as polycarbonates, nylons and investment casting waxes.
Regardless of the type of material used, rapid prototyping processes are generally adapted to quickly and accurately deposit several thousand individual layers, each having a thickness of typically less than about 0.5 millimeter, and fuse the deposited layers to form a desired prototype. Computer data and a machine controller controls the entire process such that only selective portions of the material are cured or fused in order to achieve the desired geometry for a given prototype.
While the fabrication of prototypes in the above manner eliminates the requirement for prototype tooling, further improvements in process efficiency would be desirable. A significant shortcoming of prior art rapid prototyping techniques is the common requirement that the prototypes be sintered and cooled within a processing chamber containing an atmosphere that will not oxidize, and therefore weaken, the sintered prototype. Cooling generally requires several hours, during which time a suitable nonoxidizing gas is flowed through the processing chamber. Consequently, the chamber is nonproductive during the cooling phase of the process, such that the overall efficiency of the process is significantly reduced.
Accordingly, it would be desirable if a rapid prototyping process existed by which a prototype could be fabricated from fused materials, yet avoided the requirement of employing a single chamber for all of the steps entailed in the process.